﻿THE CATTLE GRUBS OR OX WARBKES 



57 



DURATION AND DEVELOPMENT OF THE FIFTH STAGE 



Immediately after molting, the larvse are more or less translucent 

 and the integument comparatively tender. The spiracles at first ap- 

 pear more or less iridescent and are yellowish with a slight orange 

 tinge. Growth in this stage is rapid. ' The integument becomes 

 heavier and tougher and the spiracles darker. This darkening 

 begins on the rims and gradually the entire spiracles become dark 

 brown to almost black. Along with the darkening of the spiracles 

 and the rapid growth of the larvae, there is a general darkening of 

 the entire integument. Just prior to emergence from the host the 

 grub becomes shorter and broader. Along with this change comes 

 the darkening of the integument to a deep brown or black. 



The duration of the fifth stage is extremely variable. At Dallas, 

 Tex., the minimum length of this stage in H. li'ne.aturrh has been 

 observed to be between 18 and 21 days. More than 100 larvse were 

 observed. In another instance there was a period of from 19 to 21 

 days, but it appears that very few complete this stage in less than 23 

 days. The average, based on 71 records made at Dallas, Tex., was 

 30.3 days. Some of these records are given in Table 7. 



The length of the fifth stage was recorded in six larvae of H. 

 Jineatum at Herkimer, N". Y. The maximum was 47 days, the 

 minimum 29 days, and the average 38.5 days. In 1922 in Orange 

 County, N. Y., the length of the instar was detennined in 19 larv^se. 

 The maximum was 39, the minimum 16, and the average 29.5 days. 



The duration of the fifth stage of II. tovis was determined in the 

 case of 58 larvse at Herkimer, N. Y., in 1921, and in the case of 19 

 larvse at Middletown, N. Y., in 1922. The maximum, minimum, and 

 average in the former were 62, 26, and 39.6 days, and in the latter 45, 

 35, and 40.1 days. Some of these records are presented in Table 6. 



Table 6. — Duration of fifth star/e of Ilypoderma 'bovis in New York, 



Locality 



Larvae 

 molted 

 to fifth 

 stage 



Mature 



larvae 



emerged 



from 



liost 



Dura- 

 lion 

 of 

 fifth 

 stage 



Locality 



Larvae molted to 

 fifth stage be- 

 tween dates 



. Mature larvae em- 

 erged from host 

 between dates 



Dura- 

 tion 

 of fifth 

 stage 



Herkimer 



Do 



Do 



Do 



Do 



Do 



Do 



Do 



Do 



Do 



Do 



Do 



Do 



Do 



Do 



Do 



Do 



Do 



1921 



May 13 

 May 18 



...do 



May 19 



...do 



...do.... 

 May 21 

 May 2r, 

 May 27 

 May 31 

 June 2 

 Juno 4 

 June 

 June 9 

 June 10 



...do. . 

 June 27 

 June 29 



1921 



June 27 

 June 20 

 June 18 



...do 



June 14 

 June 28 

 July 4 

 June 20 

 July 4 

 July 7 

 July '14 

 July 16 

 Aug. 7 

 July 17 

 July 20 

 July 2.5 

 Auk. 4 

 Aug. 



Days 

 4.5 

 33 

 31 

 30 

 26 

 40 

 44 

 26 

 38 

 37 

 42 

 42 

 02 

 38 

 40 



ir, 



38 

 41 



Middletown 



do 



do 



do 



do 



do 



do 



do 



do 



do 



do 



do 



do 



do- 



do 



do 



do 



do 



1922 



Apr. 1 and 3 



Apr. 10 and 13 



Apr.l9and20 



Apr. 24 and 22 



Apr. 22 and 24 



do.. 



Apr. 2.5 and 26 



Apr. 26 and 27 



do. - 



1922 



May Hand 13 



May 20 and 24 



June 1 and 3 



June 3 and 5 



May 31 and Junes. 



June 1 and 3 



Juno 7 and 9 



June 5 and 7 



June7and9 



do 



do.. 



JuneSando 



do 



June 5 and 7 



Juno 7 and 9. 



Juno 12 and 14. ... 

 June 14 and 16 . . 

 Juno 19 and 21 



Days 

 38 to 42 

 37 to 44 

 42to45 

 42to45 



37 to 42 



38 to 42 

 42 to 4,5 



39 to 42 

 41to44 



Apr. 26 and 28 



do 



Apr. 27 and 28 



do 



Apr. 29 and M ay 1. 



May 1 and 2 



May 4 and .5 



May 5 and 6 



May 12 and 13 



40to44 

 40 to 44 

 30 to 39 

 36 to 39 



35 to 39 



36 to 39 



38 to 41 



39 to 42 



37 to 40 



It is in this fiftli or last larval stage that stockmen usually observe 

 the presence of the grui)S, as the sizi-s of the linni>s increase with the 

 growth of tlie larvy;. The sizes of tlic openings tlu-ougli tiie skin 



